As negotiators raced to hammer out a climate change agreement in Paris, countries reported progress on some key issues after two days of ministerial meetings but the issue of differentiation between developed and developing nations remained unresolved and the biggest hurdle to a pact.

US Secretary of State John Kerry flew into Paris Tuesday evening to give a push to the negotiations and held bilateral talks with India’s Environment Minister Prakash Javadekar. Differentiation is learnt to have figured prominently in their discussions.

After the Kerry-Javadekar meeting, President Barack Obama called up Prime Minister Narendra Modi. In New Delhi, the Prime Minister’s Office, in a statement, said: “The conversation focused on the ongoing Conference of Parties (CoP21) in Paris. Both leaders underscored their strong commitment to address issues related to climate change being discussed in the Paris conference through constructive engagement, without impeding the progress of developing countries. They agreed to stay in regular touch.”

A new draft text was to emerge by early afternoon Wednesday, based on suggestions and recommendations of countries during the ministerial-level consultations held on Monday and Tuesday, but it had to be put off until evening because of disagreements.

Developing country negotiators said they had “heard” that this draft text, the first to come out this week, was going to be “lop-sided” and not entirely reflective of the concerns of all the countries. They said the big thing to look for in the draft text was whether it adequately addressed the concerns on differentiation.

Differentiation refers to a principle called Common But Differentiated Responsibilities (CBDR) enshrined in the 1994 UN Framework Convention on Climate Change (UNFCCC), sort of a Constitution for the ongoing negotiations. It seeks to put greater responsibility for taking actions on climate change on a group of rich and industrialised countries whose emissions over the last 100 years is known to be the primary reason for global warming.

On Tuesday evening, at the stocktaking of the progress being made in the ministerial meetings, Vivian Balakrishnan, the minister from Singapore who was appointed to facilitate discussions on differentiation, said the countries seemed still not ready to place their final positions on this issue on the table.

Developing countries are demanding that developed nations do everything that they are mandated to do under the UNFCCC — take greater emission reductions, provide money to help the poor and vulnerable nations deal with climate change, transfer technology that will help these countries to move to a low-carbon economy, and support them through capacity building to adapt themselves better.

Developing countries are also asking that the review of country actions on climate change be differentiated — it should be stricter for developed countries.

“The next 48 hours are going to be extremely crucial. Let us see how it goes,” Javadekar told reporters.

The issue of whether the world should strive to restrict the temperature from rising beyond 2 degree or 1.5 degree from pre-industrial times has also been reopened. But negotiators said there was unlikely to be any haggling on it. A commonly agreed reference could easily be introduced in the agreement, they said. The Norwegian minister who was facilitating talks on this issue said most countries were willing to allude to a 1.5-degree target in some form in the agreement.